The present invention relates to an individual coil type ignition coil for use in an internal combustion engine which is prepared for every ignition coil each of an internal combustion engine and is used by directly connecting to said respective ignition coil.
Recently, an individual ignition coil type ignition coil for use in an engine has developed such an ignition coil is individually and directly connected to each of the ignition coils which are introduced to plug holes of the engine.
In this kind of the ignition coil, a distributor becomes unnecessary, as a result at the distributor and a high tension cord for the distributor etc. a supply energy for the ignition coil does not fall down. In addition to these, without a consideration about a fall down of the ignition energy, it can design the ignition coil. Accordingly, a coil capacity can be made small and a small scale of the ignition coil can be devised, and further by an abolishment of the distributor, a rationalization of a component mounting space in an interior portion of an engine room can be devised.
In the above stated independent ignition type ignition coil, so as to mount the ignition coil by introducing at least a part of the ignition coil against to a plug hole, it is called as a plug hole type ignition coil. Further, so as to insert a coil portion to the plug hole, the ignition coil is called as a pencil type ignition coil which is long and thin in a pencil shape. This pencil type ignition coil has a center core (a magnetic core in which plurality of silicon steel sheets are laminated), a primary coil and a secondary coil at an interior portion of a long and narrow cylindrical shape coil case.
The primary coil and the secondary coil are wounded to a respective bobbin and are arranged concentrically at a periphery of the center core. In the coil case for receiving the primary coil and the secondary coil, by potting and hardening an insulation resin and by filling up an insulation oil, thereby an insulation performance of the ignition coil is guaranteed.
As the prior arts, for example, there are Japanese application patent laid-open publication No. Hei 8-255,719, Japanese application patent laid-open publication No. Hei 9-7,860, Japanese application patent laid-open publication No. Hei 8-97,057, Japanese application patent laid-open publication No. Hei 8-144,916 and Japanese application patent laid-open publication No. Hei 8-203,757.
Among this kind of the individual ignition type ignition coil, in a system in which an insulation resin (for example, an epoxy resin) is potted and hardened in a coil case, it is unnecessary to take an oil enclosing (an oil sealing) countermeasures as shown in an insulation oil system and further the constituting members such as a center core, bobbins and coils are fixed naturally only by burying them to the insulation resin. Accordingly, the fixture of these constituting members is carried out easier than that of the insulation oil system and it is estimated that the simplification of the whole apparatus and the easy handling property can be attained.
However, to the insulation resin potted (filled up) among the constituting members of the ignition coil, a thermal stress (a heat shock) in accordance with a difference in coefficient in linear thermal expansion between these constituting members is added, it is necessary to take the countermeasures to prevent the cracks according to the heat shock. In particularly, since the individual ignition type ignition coil mounted in a plug hole of an internal combustion engine is suffered to the severe temperature condition (xe2x88x9240xc2x0 C.-130xc2x0 C.), the insulation resin must be to endure this heat shock.
The crack occurrence causes the insulation destroy by a following fact. For example, in a case of a system in which a center core, a secondary coil and a primary coil are installed from an inner side of a coil case in order, namely in a secondary wire being arranged inside a primary wire coil structure, when the air gap portion occurs between the secondary coil and the center core having the potential difference and also between the secondary coil and the primary coil having the potential difference according to the cracks, the electric field concentration in which the electric field strength of the air gap portion becomes extremely large occurs and thereby the insulation destroy occurs.
As the countermeasures for the crack prevention, by adjusting the bobbin material for constituting the coil portion of the ignition coil and the blending rate of the filler etc. in the insulation resin, it is taken the consideration in which the coefficients in linear thermal expansion of these members are approached to those of the center core and the coil, etc.
An object of the present invention is to provide an individual ignition type ignition coil which is mounted in a plug hole and is suffered to the severe temperature environment wherein by heightening the close adhesion strength (the bonding strength) between a bobbin and an insulation resin an anti-heat shock can be improved and also by attaining the crack prevention and the peeling-off prevention of the insulation resin an improvement of the insulation performance can be obtained.
Further, by heightening the anti-heat shock and the insulation performance as stated in the above, a requirement for a slim size diameter of a pencil type ignition coil (a slim shape cylindrical shape ignition coil) which is mounted in a plug hole is satisfied.
So as to attain the above stated object, the present invention proposes basically a following means for solving the problems.
Namely, in an individual ignition type ignition coil for use in an internal combustion engine in which a center core, a primary coil and a secondary coil are installed concentrically to an interior portion of a coil case, a coil portion is provided by filling up an insulation resin among these interior constituting members, said ignition coil is connected directly to a respective ignition plug of the internal combustion engine, the individual ignition type ignition coil for use in the internal combustion engine, wherein between said primary coil and said secondary coil, at least said secondary coil is wound on a synthetic resin bobbin, on a surface of said bobbin, a skin layer is removed, and to said surface of said bobbin, said insulation resin is adhered closely.
The present invention can be adopted to the individual ignition type ignition coil wherein the secondary wire being arranged inside the primary wire ignition coil structure in which the secondary coil is arranged inside the primary coil (the system in which the center core, the secondary coil, the primary coil are arranged from the inner side of the coil case) and also to the individual ignition type ignition coil wherein a secondary wire being arranged outside a primary wire ignition coil structure in which the secondary is arranged outside the primary coil (the system in which the center core, the primary coil, the secondary coil are arranged from the inner side of the coil case).
Herein, the reason why the bobbin to be subjected to the skin layer removal is made the bobbin of a side of the secondary coil (the secondary bobbin) as the necessary and the minimum is that since the secondary coil is required to form the minute winding it is necessary to wind the secondary coil through the bobbin. Namely in the secondary coil the winding layer is destroyed, it causes a state in which the wires having the large line voltage approach with together and by this fact in which according to the line voltage exceeding the anti-voltage of the windings (the anti-voltage performance of the enamel for covering the coil) since the insulation destroy causes, therefore the minute winding is required.
On the other hand, in the primary coil since the whole primary coil has the ground voltage, the insulation destroy caused by the above stated line voltage does not cause, it does not require the minute winding and also it is not always necessary to wind the primary coil through the bobbin. For example, in a case of the secondary wire being arranged outside the primary wire ignition coil structure (the system in which the secondary coil is arranged outside the primary coil), the primary coil is wound directly to the center core through an insulation sheet.
According to the present invention, following operations and effects will be expected.
In a case where the secondary bobbin is made of the synthetic resin, the filler is mixed with the bobbin as the auxiliary material, in common a surface of the bobbin is covered by a smooth skin layer (a resin covering layer) and bellow this the mixture layer of the filler and the resin exists. In the present invention, this bobbin surface is performed in advance by the roughness treatment (a satin treatment, namely the surface treatment having the rough feel) according to the blast treatment, for example, and then the skin layer is removed and the filler is exposed under the uncovered condition on the bobbin surface.
The secondary coil is wound on the above stated bobbin in which the skin layer has removed and further this secondary coil and the secondary bobbin are installed at the interior portion of the coil case together with the primary coil and the center core etc., and also the insulation resin is filled up among these constituting members.
Since the insulation resin is closely adhered to the secondary bobbin surface (the filler uncovered face) having no skin layer, the close adhesion strength (the bonding strength) by the anchor effect according to the twining to the filler is increased, then the anti-heat shock of the insulation resin is heightened remarkably and the crack occurrence in the insulation resin and the peeling-off against the bobbin are prevented. As a result the insulation performance between the secondary coils together and among the secondary coil and other constituting members (for example, the primary coil, the center core etc.) can be heightened.
Further, in the cases where the peeling-off in the insulation resin and the cracks occur, a mechanism of the insulation destroy will be explained in detail in a latter carrying-out embodiment item.